In a sheet-metal rolling mill it is frequently necessary to roll a band of sheet metal up into a large-diameter coil that may weigh up to fifty tons, and at a later time to unroll this coil. Only in coil form can such bands of sheet metal be conveniently stored or warehoused temporarily between stretching, pickling, and other operations.
Thus it is necessary in such mills to provide devices for rolling up the sheet metal and for holding the rolled-up coils securely while they are being unrolled. Such an apparatus typically has a winding stem or core whose longitudinal axis extends horizontally and which is at least limitedly radially expansible. In this manner it is possible to expand the core to its maximum diameter prior to winding a band thereon so that the finished coil can be removed from the core readily once the diameter of this core has been reduced. The core may also be fitted into a wound-up roll and expanded so as tightly to hold this roll and to center it on the shaft axis.
To this end the core is usually subdivided along a plurality of axially extending planes into a plurality of angularly spaced segments that may be displaced radially from an outer position where all of the part-cylindrical outer surfaces of the segments lie on a common cylinder centered on the segment to an inner position. It is clear that in such an arrangement a generally cylindrical surface, albeit provided with angularly spaced gaps, is only formed in one position of the segments. It is therefore necessary to provide a separate core element for each difference size coil to be wound or unwound. Furthermore the gaps between the segments usually telegraph through at least the first layers of band wound around the core so that the end of the band when unwound carries a succession of transverse bends that often make this section of the band useless.
The several segments are often displaced radially by means of a complicated camming or lever arrangement between a horizontal support shaft and the segments. This reduces the maximum possible diameter of the support shaft so that a relatively weak structure is produced. Other mechanisms using complicated hydraulic arrangements or two-arm levers are also known, all being relatively complex and taking up considerable space within the support core.
It is also known to support this core at both ends, or to employ a two-part core for supporting the coil. Such mechanisms are considerably stronger than the above-described types, but are also much more expensive and prone to failure. Also in such systems, the changing of the internal diameter on the coil is a relatively complex procedure often requiring considerable downtime of the machine.
Another disadvantage of these devices is that the radially spreadable segments are not securely attached to the central support shaft. Thus when the core is rotated at high speed without a coil in place the segments can fly outwardly thereby ruining the machine and injuring a nearby machine operator.
Not only must the apparatus be able to support the roll, but it must frequently be able to exert on the roll tensions of up to twenty tons in order to stretch or roll the band properly. Thus it is necessary that the coil be securely joined to the core by forcing the radially spreadable segments very tightly against the inside of the coil so that the internal actuating mechanism for these segments must be rugged in the extreme. Another difficulty with such systems is that the heavy-duty actuating mechanism of each such core is so very complicated that changing of cores when different size coils must be held is a complicated operation requiring considerable time.